1. Technical Field of the Invention
The present invention relates to an exhaust gas purification apparatus.
2. Description of Prior Arts
Development of a lean NOx catalyst as a catalyst for effectively purifying NOx in lean burn combustion exhaust gas in which oxygen coexists is progressed, and a catalyst which traps NOx on an adsorbent once, and then performs reduction purification of the trapped NOx is developed and its adoption is being expanded.
Upon mounting this lean NOx catalyst on a diesel vehicle which performs lean combustion, a working temperature of the catalyst does not necessary cope with the temperature of exhaust gas of the diesel engine. That is, the exhaust gas of the diesel engine is low in temperature by about 100° C. than that of a gasoline engine, so that NOx in the exhaust gas is not necessary effectively purified by the same layout and use manner as the gasoline engine. Therefore, a method of optimizing the temperature of lean NOx catalyst by using a heat accumulator, is disclosed in JP 11-125113 A.
Further, in the diesel engine, fuel is injected directly into the combustion chamber, so that particle-shaped substances which are called particulates (PM) are generated. PM comprise soot generated from fuel having not contacted with air during fuel combustion, SOF (soluble organic fraction) caused by fuel impinged on a wall of apparatus or the like and lubrication oil, sulfur oxides generated from sulfur in the fuel, etc. PM cause sever injury in respiratory organs and are substances which are unavoidable to be purified in purification of diesel exhaust gas.
As PM reducing measures, there is a method of trapping PM with a filter which is a diesel particulate filter (DPF), and regenerating the filter by burning PM when pressure loss of the filter increased by accumulation of PM.
A method of using a heater to burn PM trapped by DPF is disclosed in JP 2001-73748 A or JP 9-137716 A.
[Patent Literature 1]    JP 11-125113 A
[Patent Literature 2]    JP 2001-73748 A
[Patent Literature 3]    JP 9-137716 A
[Patent Literature 4]    JP 10-212933 A
[Patent Literature 5]    Japanese patent No. 2600492
In the method of JP 11-125113 A, a heat accumulator is provided only on the outer periphery of a NOx catalyst, JP 11-125113 A is silent on heat utilization in the other construction as described later.
JP 2001-73748 A and JP 9-137716 A each are silent on temperature raising of the other construction by utilizing combustion heat of PM, as described later.